Method and apparatus for analyzing particulate matter

ABSTRACT

An apparatus for analyzing particulates including solutes in a sample liquid suspension in which the sample liquid suspension flows through an aperture into a first region of a reservoir containing particle free liquid to form a jet which entrains particle free liquid to ensheathe the jet. The jet passes through a muffler which includes a funnel and a throat into a second region of said reservoir where the particle free liquid and particulates are mixed. The throat is configured to prevent regurgitation of liquid from the second region back into the first region. A return passage connects the second region of the reservoir to the first region. The energy of the jet stream causes liquid to flow from the second region to the first region to provide particle free liquid to the first region. The return passage is configured or contains means to continuously mix the advancing liquid to prevent central streamers and the peripheral Coanda effect. This assures that during particle analysis only clean liquid reaches the first region, and that during cleanout particle free liquid admitted into the first region displaces all analyzed sample liquid without carryover.

REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Provisional Application Ser. No.60/006,917 filed Nov. 17, 1995.

BRIEF DESCRIPTION OF THE INVENTION

This invention relates generally to a method and apparatus for analyzingparticulate matter and more particularly to an improved method andapparatus for obtaining signals from particles or solutes which travelthrough an aperture and sensing regions without interference fromextraneous particulates.

BACKGROUND OF THE INVENTION

There are many types of particle counters. This invention evolved fromparticle counters of the type commonly known as a Coulter counter. U.S.Pat. No. 2,869,078 describes a counter in which a suspension ofparticles to be counted flows from an upstream vessel through anaperture to a downstream vessel. An electrical current is establishedthrough the aperture by electrodes placed in each of the vessels. Thedisplacement of fluid by a particle in the sensing zone of the sensingaperture causes a change in impedance in this passage. That change inimpedance causes a change in current or in voltage which is detected bya suitable detector. The particle laden fluid is caused to flow throughthe aperture into the downstream vessel by application of a differentialpressure such as by withdrawing liquid from the fluid-filled andotherwise closed downstream vessel. The volume of liquid which leavesthe closed downstream vessel through an outflow port equals exactly tothe volume of liquid traveling through the sensing aperture. By countingthe particles as a predetermined volume of fluid leaves the closeddownstream vessel, one can obtain the concentration of particles in theparticle laden fluid in the upstream vessel.

In the early Coulter particle counters, the downstream vessel quicklybecame contaminated by analyzed waste and there were no attempts to letonly clean fluid reach the sensitive region at the downstream side ofthe sensing aperture. As a result extraneous particles traveled intothat sensing zone and gave rise to extraneous signals and to a buildupof deleterious precipitates. U.S. Pat. No. 3,299,354 provided anadditional downstream chamber with an elongated snout having a largecapture orifice placed opposite the much smaller sensing aperture. Thethin fluid jet formed by the flow of particle laden fluid through thevery small sensing aperture was directed into the large capture orifice.The intent was to trap all of the suspended and dissolved particulates.However, according to later patent applications assigned to the assigneeof that patent, because of eddy currents and other irregularities, allparticulates were not captured by the snout, extraneous counts werestill generated at the sensing orifice, and it proved essential to use aburn circuit to keep the rear of the sensing orifice free of particulateprecipitates. U.S. Pat. No. 3,746,976 describes an apparatus employingtwo downstream chambers with an elongated capture snout opposite thesensing aperture. A pump disposed between the two downstream chambersrecirculated fluid through a filter to the sensitive zone at thedownstream side of the sensing aperture. The action of the pump was toprovide clean fluid to hydrodynamically focus the thin particle ladenjet from the sensing aperture so that it passed through the firstdownstream chamber and on through the capture orifice without any of thesample suspension remaining in the region of the sensing aperture, orbeing able to return to that region. U.S. Pat. No. 4,360,803 is directedto a similar particle analyzing apparatus in which the fluid isallegedly pumped only by the kinetic energy of the thin jet from thesensing aperture and this jet is alleged to be hydrodynamically focusedthrough the large capture orifice. Once one computes the fluidicresistances and pressure gradients in the recirculation circuits andacross the capture orifices of any of the structures taught in '803there is certainly insufficient kinetic energy in the thin jet from thesensing aperture to accelerate the entire merry-go-round cycle throughthe large capture orifice to beyond the velocity of the incoming jet.Hence, compared with dimensions and velocities of the sample stream jetat the exit of the sensing aperture, there can be no net sample streamacceleration or diameter contraction at the passively functioningcleaning orifice; hence no hydrodynamic focusing. Indeed, despiteentrainment of much clean fluid by the thin fluid jet from the smallsensing aperture, the resulting expanding, fluttering, ensheathed samplejet is still so small relative to the large capture orifice that itpromotes intermittent counter current streams of contaminated fluid toperiodically emerge from the capture snout to the sensitive region ofthe sensing aperture.

The pressure built up in an expansion chamber to create a fluid flowfrom that chamber is the classic head (static) pressure which alsobehaves as a backpressure at the entrance to the expansion chamber. Thisbackpressure is well documented in the literature on combustion enginesand fan efficiency. In axial fans, it can cause the fluid near the hubto move in the wrong direction through the fan. In the cited particlecapture arrangements the head pressure forces waste fluid to flow downthe fluctuating pressure field to periodically jet waste contaminantsright back out of the "cleaning orifice" and right into the rheologicsump adjacent to the jet emerging from the sensing aperture and withinthe internal electric fringe field of the "closely spaced" sensingaperture.

U.S. Pat. No. 4,710,021 describes a particulate matter analyzingapparatus in which the original downstream vessel of the Coulter counteris a closed chamber partitioned into two regions, proximal and distal,by a barrier which includes a large capture orifice directly oppositethe small sensing aperture formed in the wall of the chamber. The thinsample jet emerging from the small sensing aperture travels through theproximal region of the divided chamber, on through the large captureorifice, and strikes the opposite (distal) chamber wall where it wasbelieved that the kinetic energy was dissipated. However, detailedstudies have now shown that as a result of the Coanda surface floweffect, particulate matter rapidly travels along the walls of the distalchamber regions, all faces of the barrier, and the walls of the proximalchamber. Thus particulates and solutes rapidly reach the sensingaperture where they generate extraneous signals and soon dispersethroughout the proximal region of the partitioned chamber.

Apparatus exploiting this invention for better resistivity leukocyteanalysis has also had to resort to a so-called burn circuit to keepparticulate debris from building up in the sensitive region on thedownstream side of the sensing aperture. Additionally, Coanda effectcontamination throughout the proximal region of the divided chamber hasbeen too high to permit the envisioned exploitation of the regionbetween the sensing aperture and the capture orifice for opticalinterrogations of the particles or solutes in the thin sample jet.

In addition, because of the necessarily large size of the barrierorifice, there is a tendency for regurgitation of particulates throughthe orifice via well known countercurrents. Even with the bestmanufacturing tolerances, a precise axial alignment of the sensingaperture and cleaning orifice can not always be achieved resulting inonly a fluttering portion of the sample jet being captured if thecapture orifice is made smaller. On the other hand, if the captureorifice is enlarged, this leaves more area for direct regurgitation ofparticulates driven by the kinetically unopposed head pressure explainedabove.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedanalyzing apparatus for analyzing liquid samples carrying suspendedparticulate matter such as particles or solutes.

It is another object of the present invention to provide an apparatus inwhich fluid displacement at its inflow or outflow is a measure of thevolume traversing each sensor and which apparatus forms a jet stream ofsample which travels through a particulate free liquid region where itcan be sensed and analyzed.

It is a further object of the present invention to provide a particulatematter analyzing apparatus in which the particulate matter flows throughan orifice or aperture to form a jet stream with entrains uncontaminatedproximal priming fluid which travels to a distal region which traps theparticulate matter and prevents it from interfering with measurementsmade at the inflow aperture.

It is a further object of the present invention to provide a particulatecounter/or analyzer apparatus in which a particulate laden sample fluidintermittently flows from a sensing aperture to form a jet which travelsthrough a particulate free liquid and a high resistance communicationpath into a dynamic fluid trap so that, through sample containment andenergy damping or harnessing in said fluid trap, the region immediatelyaround the sensing aperture is kept clear not only of undesirable fluiddynamics or other fluidically generated energy fields, but also ofparticles and solutes carried in the particulate laden sample.

It is another object of this invention to provide an apparatus in whichsamples and reagents are mixed thoroughly in a dynamic fluid trap whichthey enter in the form of a joint jet.

It is a further object of this invention to provide a reagent primedfluid region into which sample is jetted together with Venturi scavengedpriming reagent, through a high-resistance communication path and fromwhich priming reagent can return by a low-resistance return path tosatisfy the Venturi needs of the sample jet and in which low-resistancereturn path neither axial or core streamers nor peripheral orwall-hugging Coanda effect jets can result in macro heterogeneous flowof the leading priming fluid and the following displacement fluidconsisting of sample mixed thoroughly with priming fluid.

It is another object of the present invention to provide an apparatus inwhich all the material in a particulate laden jet is captured in a fluidscavenging and flow rate damping silencer so that a reliably clean andfluidically quiet sensing environment is created for resistivity,optical and other interrogation of particles or solutes carried in thejet.

It is another object of this invention to provide a structure in whichtendencies for particles and micro bubbles to accumulate are overcome bya design which facilitates efficient cleanout between every duty cycle.

The foregoing and other objects of the invention are achieved by anapparatus which includes a closed reservoir primed with clean liquid andhaving an entry aperture which communicates with the first or proximalregion to which particulate laden sample fluid flows to form a jet, amuffler, the entry funnel of which is positioned to receive the jet anddirect it through a throttling throat into a second or distal regionwhere the concentration of the particulates and the kinetic energy arediluted through efficient mixing and from which region astreamer-preventing and Coanda flow opposing conduit provides a flow ofliquid back to the first or proximal region and an exit port allowssample to enter the closed reservoir at the entry aperture by allowingan identical volume of displaced fluid to leave the closed reservoirfrom the exit port.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects of the invention will be more clearlyunderstood when read in conjunction with the accompanying drawing ofwhich:

FIG. 1 is a schematic diagram showing a sample cuvette, electrolytereservoir or chamber, fluid flow control valves and associated systemcontrolling and signal processing electrical circuits.

FIG. 2 is an enlarged view showing the electrolyte reservoir or chamberand sensing aperture of FIG. 1.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a sectional view of another embodiment of an electrolytereservoir and sensing aperture showing the flow of electrolyte andsuspended particulates during the analytical counting phase of anoperating cycle.

FIG. 5 is a sectional view of the reservoir of FIG. 4 showing flow ofclean electrolyte during the phase of the operating cycle when theaperture and electrolyte reservoir are cleaned and primed for analysisof the next sample.

FIG. 6 shows an end view of the apparatus shown in FIGS. 4 and 5 lookingthrough a transparent end cover.

FIG. 7 shows a photo-electric sensor for sensing of particulates in theclean sample jet stream.

FIG. 8 shows a laser beam and transducers for analyzing particulates inthe clean sample jet stream.

FIG. 9 is a sectional view of another embodiment of the inventionshowing a sample cuvette and an electrolyte reservoir with controlledflow of priming electrolyte and suspended particulates during a countingcycle.

FIG. 10 is a sectional view taken along the line 10--10 of FIG. 9.

FIG. 11 is a sectional view taken along the line 11--11 of FIG. 9.

FIG. 12 is a sectional view taken along the line 12--12 of FIG. 9.

FIG. 13 shows a sensing aperture tube embodiment of the invention.

FIG. 14 is a top plan view taken along the line 14--14 of FIG. 13.

FIG. 15 is a sectional view taken along the line 15--15 of FIG. 13.

FIG. 16 is a sectional view taken along the line 16--16 of FIG. 13.

FIG. 17 is a sectional view taken along the line 17--17 of FIG. 13.

FIG. 18 shows another sensing aperture tube embodiment of the invention.

FIG. 19 is a sectional view taken along the line 19--19 of FIG. 18.

DESCRIPTION OF PREFERRED EMBODIMENT

In common with prior art, one embodiment of the present invention countsand analyzes suspended particles by causing a sample suspension to passthrough a sensing aperture through which an electric current is alsopassed. The suspended particles change the impedance through theaperture and modulate the electric current or voltage. Particulates arecounted and sized by processing the electric current or voltage.Generally, the particulate containing solution is disposed on one sideof the sensing aperture and a clean electrolyte is on the other side ofthe aperture. A pressure differential causes a predetermined volume ofthe sample suspension to pass through the aperture and the particulatesare counted to give a measure of particulate concentration in thesample. The electrical current or voltage waveform may be analyzed togive an indication of size, shape and composition of the particulates.In other embodiments, the aperture through which the sample fluid ispassed is not used as an electrical impedance sensing aperture. Instead,the suspended particles and even solutes in a suspension which maycomprise particulates down to the size of molecules arephoto-electrically sensed by absorption or reflection of light or byflorescence, phosphorescence and analogous interactions of matter withan interrogating energy field through which the unadulterated sample isunidirectionally passed.

FIGS. 1-3 show one embodiment of the invention. The sample suspension isreceived in cuvette 11. An electrolyte reservoir or chamber 12 havingproximal region 12a and distal region 12b connected by a muffler 13a,bis coupled to the cuvette 11 through a sensing orifice or aperture 14.An elongated passage 15 acts as a fluid capacitance as part of the fluidreservoir 12 and provides controlled fluid communication between theregion 12a and 12b. The region 12a serves as the analyzing region andwill be described in more detail hereafter. The passage 15 is alow-resistance return path which counteracts axial streamer formationand surface Coanda flow advances as will be described in more detaillater. Together with the muffler 13a,b, and the flow control mechanismbuilt into the fluid conduit 15, the region 12b serves to dynamicallytrap particulates and to damp and/or harness the kinetic energy of thefluid jet from the analyzing aperture. The aperture 14 may be formed ina jewel 16 which is suitably secured to the body of the reservoir 12.The reservoir or chamber 12 is initially filled with a particulate freeor solute free electrolyte or liquid via a fill tube 17 connected to arinse electrolyte or fluid system 18 via valve 19. The reservoir orchamber 12 is filled and cleaned with clean electrolyte or liquid byopening inlet valve 19 and outlet valve 21a connected to a vacuumreservoir 22 through a volume metering system 23. Valves 19 and 21a areclosed after the reservoir is filled with clean electrolyte or primingliquid. The reservoir is designed, in part, as a serpentine conduit tofacilitate complete filling without air or bubble entrapment. Valve 21bis now opened momentarily to atmosphere. This introduces an air segmentfrom valve 21b to beyond fluid volume metering manometer 23 leaving afluid meniscus at the end of the fluid filled line segment from exitport 20 through valve 21a to junction 21c. During this time, the cuvetteis filled with the sample suspension from the supply system 24 which canbe an automated dilution mechanism for an originally highly concentratedsample like whole blood. Because, during this operating phase, reservoir12 is a closed fluidic system except at the entry aperture 14 and theexit port 20, when valve 21a is now opened to initiate flow through thesensing aperture 14, stable sample flow is soon established throughproximal region 12a as detailed below. During the settling period forthis initial flow, a voltage is applied between the electrode 25disposed in the cuvette and electrode 26 disposed in the chamber region12a. The voltage across the electrodes causes current to flow throughthe sensing or analyzing aperture 14. The flowing particulates whichmodulate this sensing field can therefore be analyzed and counted.Opening the valve 21a to connect the chamber 12 to the vacuum reservoiror source 22 initiates an analytical counting cycle. Liquid is withdrawnfrom the chamber 12 by the vacuum source 22 into the volume meteringsystem 23 which serves to measure the advance of a predetermined volumeof liquid during the flow of which particulates are analyzed and countedpassing through the sensing aperture. The metering system 23 may becomprised of photo detectors spaced along a conduit. When a liquid front(not shown but beginning at junction 21c) first reaches a first detector(not shown), counting of particulates is commenced by the signalprocessing circuit 28 and when the liquid front reaches a seconddetector (not shown), counting terminates. This general process providesthe number of electronically identifiable particles for a given samplevolume passing through aperture 14 and region 12a. This sampled volumeis equal to the volume of liquid between the photodetectors. After oneor more fluid volume measurements, the chamber 12 is cleaned by flushingit with electrolyte from system 18 via valve 19 as described above. Thereservoir is thereby also primed with clean electrolyte or diluent, thereservoir having been designed in part as a serpentine conduit tofacilitate complete recharging without carryover in the critical fluidregions from prior samples. The sample cuvette is emptied after a samplehas been analyzed by opening the valve 28 connected to the vacuumreservoir 22. After the sample is emptied, the cuvette is cleaned byintroducing clean electrolyte by further means (not shown). The valve 28is then closed and new sample suspension is introduced from the samplesystem 24.

Operation of the apparatus to eliminate interference from extraneousparticulate matter in the sensing region will now be explained withparticular reference to FIG. 2. When liquid is withdrawn from the closedchamber 12 by opening of the valve 21a, particulate laden samplesuspension is drawn through the sensing orifice at a high velocity. Thisforms a sample jet 31 which travels in a straight line towards themuffler 13. The jet stream 31 entrains clean liquid as indicated by thearrows 32. This accelerating entrained clean liquid ensheathes the jetsample stream 31. The joint jet stream of sample core and surroundingsheath is captured by the conical funnel or muffler entry horn 33 and isconstrained or throttled through the narrow throat 34. This joint jetentirely fills the high resistance throat thereby preventing anyregurgitation of particulate laden fluid back into the sensing region12a. Beyond the throat is another horn 35, 13b opening at gradual angle(ideally at subtended half angle below 8°) with optional ribs such asthe step shown at the transition 13c from piece 13a to horn continuation13b. The jet continues into the expansion and mixing region 13b, 12bwhere the kinetic energy of the core sample jet is dissipated bythoroughly mixing with the particulate free sheath and priming fluid. Inother words, by design, muffler 13a is a high-fluidic-resistance passagefrom region 12a to 12b. The joint jet entering the expansion chamber 12bthereby creates a head pressure while, in the throat and expansion horn35, 13b, the kinetic impulse of the entering fluid jet prevents directbackflow through the muffler section 13a. This establishes a sustainedpressure differential between the regions 12a and 12b so that fluid mustflow along the low-fluidic-resistance conduit 15 into the region 12a.

Although the clean and particulate laden fluid mixes intensively inregion 12a, it still possesses intense kinetic energy in the form ofheterogeneous vorticity. The effect of that is clearly apparent in thefluid front which advances from the exit port into the volume meteringmanometer 23. Because of the prior cleanout phase after the last sampleanalysis, fluid segment 20 to 21a can be arranged to commence as totallyclean fluid. However, if fluid line 20 to 23 is a typical tube likeconduit, then, even if an additional coiled delay line is insertedbetween exit port 20 and valve 21a, the waste fluid passing through themanometer is almost instantly contaminated by two dynamic mechanisms,axial core streamers and even thinner peripheral Coanda wall sheet jets.These phenomena are made clearly visible when intensely redanticoagulated whole blood or suitable dyes or inks are used as anindicator sample in cuvette 11. Both the advancing axial core streamersand the rapidly moving surface sheets can only occur through theconcurrent formation of analogous countercurrent flows of, initially,clean priming fluid. It is irrelevant to tie manometer's function thatduring the commencement of an analytical cycle, the initially cleanfluid limb 20 to 21c rapidly becomes contaminated during passage of itsleading meniscus from location 21c to 23.

If conduit 15 were a simple fluid conducting tube, whether straight orsmoothly coiled, then during the commencement of an analytic countingcycle, proximal region 12a of fluid reservoir 12 would also rapidlybecome contaminated from distal region 12b through the mechanisms ofleading axial core streamers and advancing peripheral Coanda surfacesheets. This fact is made clearly visible if, for low-fluidic-resistanceconduit 15, a smooth coil of equal length, capacity, and fluidresistance is substituted in the structure of FIGS. 1-3 or FIGS. 4-6 andthen undiluted whole blood or India ink is used as an indicator samplein cuvette 11. An essential key to this invention is that the conduit 15is designed to inhibit or control along its course both of thesediscovered heterogenising mechanisms, axial core streamers andperipheral Coanda effects. The conduit is characterized by numerousacute but smooth-contoured switchbacks. Additionally, the alternateshort straight runs of conduit 15 which are shown in section in FIG. 3can be staggered laterally in the Z direction of FIG. 2 with left rightalternation to induce further vorticity homogenizing effects across theoverall serpentine direction of flow through conduit 15. On top of that,readily available counter turning complimentary alternating fluid mixinginserts 40, such as Statomix® units, can be introduced into the entirelength of the low fluid resistance conduit 15. As a result, instead ofpiercing axial or peripheral advance jets, a uniform particulate ladenfront 36 travels along the conduit or passage 15.

Well before the front 36 reaches the area adjacent to the clean proximalregion 12a the cleaning or washing phase of the operational cycle iscommenced as described above. Both the switchback anti-demixing designof loop 15 in FIGS. 1-3 and the inline mixing inserts retain theiranti-demixing characteristics when flow is reversed for cleaning.

Thus, the present invention permits frugal, fluidically quiet, selfballasting delivery of fresh downstream fluid into a post restrictiontransducer region 12a. The invention overcomes the need to placeinterfering rigid physical boundaries into the immediate post restrictorregion or to continuously or periodically deliver very large volumes offresh liquid into that region. The present invention captures all of thematerial carried by a post constriction sample jet in the regiondownstream of the entry to the capture horn 33 of a miniaturized fluidscavenging silencer so that in region 12a, a reliably clean andfluidically quiet and stable sensing environment is created forresistivity, optical or other interrogation of particulates or solutescarried in the jet. Concurrently, a volume of fluid equivalent to thatentering the proximal region 12a in the form of the sample jet 14 leavesdistal region 12b through exit port 20.

FIGS. 4-6 illustrate another embodiment of the closed chamber. Thechamber is formed by drilling a plurality of passages 41 in acylindrical solid member 42 with cross passages 43 providingcommunication between the adjacent ends of selected pairs of passages 41so that a single continuous serpentine conduit is created withoutshort-circuiting possibilities. A cover 44 is applied to one end and amachined cover 45 is applied to the other end. Thus, the covers 44, 45cooperate with the cross passages of the cylinder to form an intenselyreflexing continuous low-resistance passageway connecting regions 12aand 12b. The cover 45 includes first passage 46 for introduction ofscavenged clean fluid into the sensing volume 12a formed between thejewel mounting member 47 and the protruding nozzle of muffler 13a.Second passage 48 provides communication to the valve 19 for the primingand washout supply of clean fluid after counting cycles. The cylindricalmember includes a conical bore 51 which represents expansion chamber 13band mixing chamber 12b. The arrows in FIG. 4 show the flow of liquidduring a measuring phase of the instrument whereas FIG. 5 shows the flowof liquid during a cleaning or filling phase. Operation of the analyzingcell, FIGS. 4-6, is the same as described in reference to FIG. 2. Thatis, the particle laden jet is ensheathed with clean fluid and travelsinto the funnel 33 through the narrow, high-fluid-resistance throat 34through expansion horn 35 over ribs 36, through continuation of theexpansion horns 13b and into the head pressure capacitor region 12b. Theconduit 15 inhibits or controls axial core streamers and peripheralCoanda effects as described with reference to FIGS. 1-3.

Referring to FIG. 7, there is shown a photodiode 53 which shines lightthrough the particle laden jet 54 with the light being received by aphotodetector 56. The photo diode-photodetector combination senses andcounts particulates in the jet stream. FIG. 8 shows a laser 57 shininglight into the jet stream 58 with the photodetector 59 receivingtransmitted light to indicate absorption by particulate matter whereasthe detector 61 senses light reflected by particulate matter and adiametrically opposed detector senses fluorescence excited by the laser57 and emitted by the particulate matter. The laser may operate at apredetermined wavelength and the particles may be tagged selectively tofluoresce in response to the light as they travel through the laserbeam.

Operation of the apparatus will now be described with reference to oneanalytical counting cycle. Before a count commences, clean fluid iscaused to fill the entire fluid region of the chamber 12 which as inFIG. 1, is bounded by entry aperture 14, cleanout valve 19 and exit linevalve 21a. When samples are processed continuously--without longinterruptions between analysis, a "miser mode" of operating the systemcan be selected and even less priming fluid is necessary. After thesystem is primed, valve 21b is opened briefly to establish the fluidmeniscus at junction 21c to facilitate the metering mechanism 23. Thesample cuvette 11 is charged with the known dilution of sample. Thevalve 21a is then opened and the orifice jet starts to flow due to theapplied differential pressure across the sensing orifice 14. Thisinitiates the jet flow from the orifice into the capture funnel 33,through the high-fluid-resistance (choking) throat 34 and into theexpansion horn, kinetic energy diffuser and mixing region 35, 13b, 12b.In one example, the strong sample jet, flowing at 15 μl/s, carries withit some 91 μl/s of pristine fluid through the throat. As the air-fluidinterface meniscus at junction 21c advances towards the volume meteringsystem 23 current is applied to electrode 26 as in the description ofFIGS. 2 and 3. Volumetric metering during the counting phase of theanalytic cycle may be by photosensors. Counting of particulates in aknown volume of fluid is initiated by the advancing meniscus triggeringone of potentially many "start sensors" and terminated when the meniscusreaches any one of potentially many "stop sensors". The volume offlowing fluid which was needed to advance the meniscus between sensorsfrom any start to any stop sensor has been calibrated previously and isthereby known very precisely. Since the start and stop meniscus andsensors are similar to each other, the systematic differences whichresult from ambient temperature changes do not affect this calibrationeven though the viscosity of water changes enormously from cold to warmlaboratory environments for an instrument. Since the sensing orifice is,in fact, a capillary viscometer, the precisely measured count timereflects this viscosity. However, the manometer volume is independent ofthis. Provided the rigorously monitored system remains stable inpressure and flow, multiples of the currently measured count timetherefore provide precisely extrapolated volume multiples below andabove the calibration volume represented by the manometer volumes. A 100μl manometer therefore permits "volumetric metering" from, say, 10 μl toover 1000 μl provided the entry aperture conditions are immune to flowrestricting deposits from the accumulating waste inflow.

During the counting phase of a 330 μl manometer analytic cycle: 2330 μlof fluid flows through the chocking muffler throat into the expansionchamber, and out of the expansion chamber into the metering andrecirculation lines; 330 μl of sample fluid flows through the entryaperture 14, through the clean sensing region 12a as sample jet, throughthe muffler as sample accompanied by 2000 μl of scavenged clean Venturifluid, from the exit port 20 as sample waste extensively diluted by thepriming and sheath fluids, and from the manometer's start sensor to themanometer's stop sensor as a front commencing as clean priming fluidwhich is however quickly contaminated by axial core streamers incombination with Coanda wall sheets of mixed waste darting ahead fromexit port 20; 2000 μl of fluid also flows from the expansion chamber at12b into the 4,320 μl capacity recirculation cyclo-labyrinth or conduit15 where it is maintained in the form of well-compacted waste, therebydisplacing 2000 μl of clean fluid into the chamber portion 12a.

Within the cyclo-labyrinth, the inherent tendency for axial streamersand Coanda surface jets to shoot continuously ahead in a straighterconduit and to rapidly penetrate to 12a is counteracted by the intensecurl and accompanying vorticity which are added by the controlledreflexive folding and acute serpentine twisting of the passages evenwithout insertion of any additional available mixing elements. Intraversing this compact labyrinth 41, FIGS. 4-6, an element of fluidundergoes continuous homogenization synchronization of mean velocitywith adjacent elements of fluid in any cross section by executing around10 three hundred and sixty degree revolutions in the cross-sectionalplane and some 5 complete three hundred and sixty degree revolutions inthe longitudinal plane. It is unnecessary to argue over whether or nottrue turbulent flow is established anywhere in this system. Relativehomogeneity of the advancing front is readily demonstrated with thedescribed indicator techniques which also demonstrate the failure ofprior attempts to solve this problem.

During the cleanout phase of the analytic cycle, as illustrated in FIGS.1 and 5, the muffler flows remain in the same direction, but the flowsin the cyclo-labyrinth are reversed. The anti-demixing design alsofunctions under reverse flow and, because the inflow of cleanout fluidis through the macro-port instead of the micro-orifice, the orderlycleanout is vigorous and rapid.

Referring to FIGS. 9-12, there are shown sectional views of anotherparticulate matter sensing apparatus. Like reference numerals have beenapplied to the like parts. The apparatus includes a cuvette 11, achamber 12 including regions 12a, 12b, interconnected bylow-fluid-resistance conduit 15, in the form of a tube 61. Cleaningvalves 19 and exhaust valves 21a are shown connected to the reservoirportions 12a and 12b respectively. In the embodiment of FIG. 9, thefluidic mixing and kinetic energy absorption at the silencer diffusionor mixing region 12b is enhanced by forming the high-fluid-resistancethroat in the muffler at an angle whereby to impart a circular vortexmotion in the expansion horn 35, 13b as the sheath-laden sample jetstream progresses to region 12b. FIGS. 10, 11 and 12 illustrateprogressive deviation of the throat passage through 13a from the centerto the side which imparts the circular vortex or rotational impetus.However, in gradually curved tubing loops of the conduit, like thoseillustrated in FIG. 9, it is necessary to insert the mixing elements 62,such as Statomix® units, along the tube to prevent axial streamers andperipheral surface sheet advances. In other respects, the embodiments ofFIGS. 9-12 operate as previously described.

FIGS. 13-17 show a further embodiment of the invention incorporated in atube 63 whose lower end is immersed into a beaker or cuvette (not shown)containing the particulate laden sample which is to be analyzed. Fluidis drawn from the closed system via the tube 71. As fluid is withdrawn,particle laden sample is drawn through the orifice 72 to form a jetwhich impinges upon the funnel 73, travels through the choking throat 74and into the expansion and diffusion chamber 76 where kinetic energy isdissipated and mixing takes place. Clean fluid circulates to theanalyzing region 77 via low-fluid-resistance conduit 78 which includesmixing elements 62 as previously described. One sensing electrode 79extends along the fluid carrying passage 81 into the region 77. Theother sensing electrode 82 extends along the sealed passage 83 into thebeaker or cuvette. A cleaning cycle is initiated by supplying fluidthrough the tube 86 and passage 81 as the fluid is withdrawn through thetube 71.

FIG. 18 shows the same analyzing apparatus with a front focusing cap 87.The cap carries a capillary tube 85 which is a fluidic resistor andreleases the particle laden fluid into the entry flow net of the sensingorifice. Passage 83 of FIG. 18 now carries both the electrode 82 andsheath fluid for hydrodynamically focusing the sample stream fromcapillary 85 through the sensing orifice.

What is claimed is:
 1. An apparatus for analyzing particulates includingsolutes in a sample liquid suspension comprising:a sample liquidreservoir for containing said liquid suspension; a particulate-freeliquid reservoir including a first proximal region and a second ordistal region forming a diffusion or expansion chamber; an aperture insaid particulate-free liquid reservoir for coupling said sample liquidreservoir to said particulate-free liquid in said first proximal region;a low-fluid-resistance passage including a plurality of acuteswitchbacks for storing fluid, conveying fluid between said first regionand second regions, and configured to counteract axial streamerformation and surface Coanda flow; a muffler including an entry funneland a throttling throat disposed in line with the axis of said aperturefor connecting the first region to the second region; and, an exhaustport connected to said particulate-free liquid reservoir whereby whenliquid is exhausted from said reservoir through said port,particulate-laden liquid flows through said aperture from said sampleliquid reservoir and forms a jet which entrains particulate-free liquidfrom said first region and travels ensheathed with particle-free liquidthrough said muffler funnel and throat into the second region where thekinetic energy of said jet thoroughly mixes the particulate-free liquidsheath and the particulate-laden liquid suspension, said ensheathed jetentering the second region also providing a unidirectional pressuredifferential between said second and said first regions so thatparticulate-free priming fluid is displaced progressively by the mixturefrom the second region through the fluid passage to said first region.2. An apparatus for analyzing particulates including solutes in a sampleliquid suspension comprising:a sample liquid reservoir for containingsaid liquid suspension; a particulate-free liquid reservoir including afirst proximal region and a second or distal region forming a diffusionor expansion chamber; an aperture in said particulate-free liquidreservoir for coupling said sample liquid reservoir to saidparticulate-free liquid in said first proximal region; alow-fluid-resistance passage including fluid mixing inserts for storingfluid, conveying fluid between said first region and second regions, andconfigured to counteract axial streamer formation and surface Coandaflow; a muffler including an entry funnel and a throttling throatdisposed in line with the axis of said aperture for connecting the firstregion to the second region; and, an exhaust port connected to saidparticulate-free liquid reservoir whereby when liquid is exhausted fromsaid reservoir through said port, particulate-laden liquid flows throughsaid aperture from said sample liquid reservoir and forms a jet whichentrains particulate-free liquid from said first region and travelsensheathed with particle-free liquid through said muffler funnel andthroat into the second region where the kinetic energy of said jetthoroughly mixes the particulate-free liquid sheath and theparticulate-laden liquid suspension, said ensheathed jet entering thesecond region also providing a unidirectional pressure differentialbetween said second and said first regions so that particulate-freepriming fluid is displaced progressively by the mixture from the secondregion through the fluid passage to said first region.
 3. An apparatusfor analyzing particulates including solutes in a sample liquidsuspension comprising:a sample liquid reservoir for containing saidliquid suspension; a particulate-free liquid reservoir including a firstproximal region and a second or distal region forming a diffusion orexpansion chamber; an aperture in said particulate-free liquid reservoirfor coupling said sample liquid reservoir to said particulate-freeliquid in said first proximal region; a low-fluid-resistance passage forstoring fluid, conveying fluid between said first region and secondregions, and configured to counteract axial streamer formation andsurface Coanda flow; muffler including an entry funnel and a throttlingthroat, said throat disposed in line with the axis of said aperture andextending off axis for connecting the first region to the second regionand mixing in said second region; and, an exhaust port connected to saidparticulate-free liquid reservoir whereby when liquid is exhausted fromsaid reservoir through said port, particulate-laden liquid flows throughsaid aperture from said sample liquid reservoir and forms a jet whichentrains particulate-free liquid from said first region and travelsensheathed with particle-free liquid through said muffler funnel andthroat into the second region where the kinetic energy of said jetthoroughly mixes the particulate-free liquid sheath and theparticulate-laden liquid suspension, said ensheathed jet entering thesecond region also providing a unidirectional pressure differentialbetween said second and said first regions so that particulate-freepriming fluid is displaced progressively by the mixture from the secondregion through the fluid passage to said first region.
 4. An apparatusfor analyzing particulates including solutes in a sample liquidsuspension comprising:a reservoir for containing said liquid suspension;a particulate-free liquid reservoir including a first or proximal regionand a second or distal region forming the diffusion or expansion chamberof a silencer; an aperture in said particulate-free reservoir forcoupling the first proximal region of said reservoir to said sampleliquid suspension; a low-fluid-resistance passage including fluid mixinginserts for storing and conveying fluid between said first region andsaid second region; and, a muffler including an entry funnel and athrottling throat disposed inline with the axis of said aperture forconnecting the first region to the second region; and means for flowingsample liquid suspension through said aperture to form a jet whichentrains particle-free liquid from said first region and travelsensheathed with the particle-free liquid through said muffler funnel andthroat into the second region where the kinetic energy of said jetthoroughly mixes the particulate-free liquid sheath and theparticulate-laden liquid suspension, said ensheathed jet entering thesecond region also providing a unidirectional pressure differentialbetween said first and second regions so that particulate-free primingfluid is displaced progressively from the second region through thefluid passage to the first region.
 5. An apparatus for analyzingparticulates including solutes in a sample liquid suspensioncomprising:a reservoir for containing said liquid suspension; aparticulate-free liquid reservoir including a first or proximal regionand a second or distal region forming the diffusion or expansion chamberof a silencer; an aperture in said particulate-free reservoir forcoupling the first proximal region of said reservoir to said sampleliquid suspension; a low-fluid-resistance passage including a pluralityof acute switchbacks for storing and conveying fluid between said firstregion and said second region; and, a muffler including an entry funneland a throttling throat disposed inline with the axis of said aperturefor connecting the first region to the second region; and means forflowing sample liquid suspension through said aperture to form a jetwhich entrains particle-free liquid from said first region and travelsensheathed with the particle-free liquid through said muffler funnel andthroat into the second region where the kinetic energy of said jetthoroughly mixes the particulate-free liquid sheath and theparticulate-laden liquid suspension, said ensheathed jet entering thesecond region also providing a unidirectional pressure differentialbetween said first and second regions, so that particulate-free primingfluid is displace progressively from the second region through the fluidpassage to the first region.